It is has been established that vascular calcification can cause stiffening of the vascular wall, reducing its compliance and lead to ventricular hypertrophy (thickening of the heart wall with reduced pumping ability), inadequate supply of blood and oxygen to the heart and heart attack. Vascular calcification is an increasingly important clinical problem particularly in the context of renal disease and diabetes type 2. It is caused by the deposition of calcium phosphate salt crystals, in the intima and/or media of arteries, with calcification at both sites common in renal disease. Calcification at either site is correlated with poor cardiovascular outcomes. Intimal calcification occurs almost ubiquitously with atherosclerosis. It's quantification using multi-slice CT scanning provides an accurate measure of atherosclerotic load that can be used to predict a patient's risk for myocardial infarction. Calcification might be involved in mechanical disruption of the plaque and may also promote inflammation by direct interactions between plaque cells and calcium nanocrystals. Medial calcification has now been identified as a major factor contributing to the high cardiovascular mortality in patients with renal failure and diabetes. It reduces arterial compliance, particularly in the aorta, leading to poor cardiac perfusion and associated heart failure. It is currently known that cardiovascular disease accounts for 48-50% of death among adults undergoing regular dialysis and patients with type 2 diabetes [USRDS 2008 Annual Data Report].
Currently available methods for the detection of vascular calcification such as plain X-ray or cardiac computed tomography (CT) scans are not sensitive enough to measure early vascular calcium load. Therefore, the existing approaches are only effectively used for patients with severe calcification, where further treatment is difficult.
The inventors have discovered that both developmental osteogenesis and arterial wall calcification is initiated by cell-derived, mineralization competent vesicles. Calcification is initiated by release from living vascular smooth muscle cells (VSMCs) of membrane-bound matrix vesicles (MV) and also by apoptotic bodies from dying cells. Vesicles released by VSMCs after prolonged exposure to Ca and P contained preformed basic calcium phosphate and calcified extensively. Importantly, in MV analysed by proteomic mass spectroscopy it was found that MV composition is regulated by VSMCs and is dependent on the environment. For example, MV released under normal physiological conditions do not calcify because they are loaded with mineralization inhibitors derived from VSMCs (matrix Gla protein) and serum (fetuin-A). Perturbation of the production or function of these inhibitors, due to different stresses and/or inflammation leads to accelerated vascular calcification. In addition, in a calcified environment, VSMCs undergo osteo/chondrocytic conversion, expressing transcription factors including Runx2 and osterix, as well as matrix proteins, which are normally restricted to bone (Reynolds J L et al., J Am Soc Nephrol. 2004 November; 15(11):2857-67; Shroff R C et al., Circulation; 2008, Oct. 21; 118(17):1748-57; Kapustin A and Shanahan C M. Curr Opin Pharmacol. 2009 April; 9(2):84-9).